Defiantly sounds like a brick but normally a psp wouldn't brick unless the user try'd to run a glitched program. but there have been cases where the psp had a viral infection from content uploaded from a memory stick or the Internet. it's very rare and i have only come across it once since ive been modding psp's. And in any case the best thing to do in this case is to mod the psp with custom firmware (CFW) or official firmware (Sony's OFW).
Using a Pandora's battery is dependable on the motherboard model of your psp. and unfortunatly the only way to find out what model your psp is is to open it. thus voiding the warrenty.
other then that you really have no choice but to replace your motherboard or send it to sony for repairs.